WowAce

Automatic ammo reloading and selection, with warnings.

Libary for cleanly inspecting other players

FuBar_GemWatchFu

Target assistance by automatic rewriting of macros

pMutilate

Persists collapsed state of headers across wow sessions.

Enhances the StackSplitFrame with numbered Buttons, a '1-Click Mode' and a 'Auto Split Mode'.

Adds tier set number and difficulty indicators to tier item tooltips.

A seperate focus bar, with focus gain prediction and rotation forecast.

Checklist and notes addon.

ElfReloaded

On login, displays changes to your guild since the last time you logged in.

Hotkey interface for spells, macros, other clickables.

Bars showing amount of buffstacks

GearRating

Replacement for the default nameplates.

Adds pipes which can control arbitary other statuses (like toggle status on key or "in combat"-state).

A death track window for Recount

A fully featured library tracking all ongoing absorb effects

DebuffEnough